a. Field of the Invention
The present invention relates generally to cargo systems for aircraft, and, more particularly, to systems for transferring and stowing cargo within the interior of an aircraft that allows for efficient and cost-effective conversion of passenger aircraft to cargo service.
b. Related Art
Historically, the commercial aircraft industry has distinguished between passenger and cargo aircraft, i.e., certain aircraft are dedicated to passenger travel while others are used solely for transportation of cargo. However, it is frequently desirable to convert an aircraft, in whole or in part, from one service to the other, the most typical example being an older passenger aircraft converted to cargo service.
A problem presented by such conversions is the difficulty in delivering the palletized cargo to the main (passenger) deck of the aircraft, after this area is cleared of seating. In a passenger aircraft, cargo is ordinarily carried in palletized form in lower deck cargo compartments. Typically, there are compartments fore-and-aft of the wing intersection/wheel well area, with each cargo compartment being serviced by a door on the lower lobe. Various types of ULDs (unit load devices) are carried in the compartments; depending on aircraft type and cargo, the ULDs may have a single line or “two abreast” configuration.
In making a cargo conversion, the ability to carry additional ULDs (as opposed to non-containerized cargo) on the main deck is an attractive option, however, it has heretofore been problematic: Carriage of ULDs on the main deck has historically required adding a large cargo door in the upper part of the fuselage, allowing direct access to the main deck; this is a major structural modification, requiring extensive reinforcement, with associated costs and regulatory approval difficulties that impact feasibility.
An alternative would be to transfer cargo from the lower lobe to the main deck (or to the two upper decks in the case of “double decker” jumbo aircraft), since the lower deck already has a cargo door, thus eliminating the requirement for a new main deck door. However, there has heretofore been a lack of satisfactory mechanisms for transferring ULDs from the lower lobe to the passenger deck/decks and vice versa. Moreover, the installation of such a mechanism, when modifying an existing passenger aircraft, presents the potential for structural and cost problems similar to those involved in installing an upper deck cargo door.
Related problems exist in certain dedicated cargo aircraft, notably double-decker “jumbo” aircraft that have been converted to full-time cargo use. For example, 747 cargo aircraft generally transport cargo on the main deck, that in passenger aircraft would carry seating, but the difficulty in raising cargo to the upper deck in the forward position of the fuselage means that this part of the aircraft frequently goes largely unused.
Accordingly, there exists a need for an apparatus for efficiently transferring cargo ULDs and similar containers between the lower area and upper deck or decks of an aircraft, so as to obviate the need to add a large cargo door in the upper part of the fuselage. Furthermore, there exists a need for such an apparatus that does not require major structural modifications of the aircraft. Still further, there exists a need for such an apparatus that, in itself, is comparatively economical, and that is physically compact so as to avoid significantly compromising the availability of space within the passenger and cargo areas of the aircraft. Still further, there exists a need for such an apparatus that is light in weight and does not require power systems that would add significant weight and cost to the aircraft in which the apparatus is installed. Still further, there exists a need for such an apparatus that operates with sufficient rapidity to avoid adding excessive time to loading/unloading operations and turnaround of the aircraft in service.